I've followed this forum for years and have always been able to repair myself up until now without asking for assistance from this fine community. My 03 TB w/ 284K miles (orig owner) has a misfire / roughness on cyl #1 that appears only at (or near) idle rpms. Mileage has dropped about 2 mpg. [I have an Autel scanner for diag.] I've swapped the Cyl #1 & #2 coils and get the same misfire on Cyl #1. As a result of the misfire, fuel trims go slightly negative. So I removed the throttle body, cleaned it (it wasn't too dirty as I did this about 50K miles prior), reinstalled, reset fuel trims with the scanner and still have the misfire at idle. Next, I replaced the (original) crankcase vent hose with the ACDelco p/n 12575660. Here is where it may get interesting...I took a piece of solid copper wire and gently slid it in the horizontal tube and it stops about 4 inches in as if I am hitting the aluminum casting. The tube portion seems wide open without any restriction using the copper wire probe method. I sprayed some cleaner in the tube, then attached a long hose to blow by mouth. It's very hard to detect if there is any orifice opening. Is it very small and undetectable using this method? I also took a battery/portable compressor, set it to 5 psi and attempted to blow through the orifice with undetermined results. Does anyone know how large the orifice opening is? By the way, when I remove the oil cap I really don't detect any suction on my palm with the motor running. Thanks in advance!